For conventional storage systems, charges are set according to the capacity allocated to a user or the volume of data used by the user. In recent years, storage systems have come to include deduplication technology that retains only one data entity for data used by a user and further maintains a data entity index indicative of data entities for data of the same content.
Storage systems adopting such data deduplication technology are distinctive in that data of the same content consumes significantly less storage space than data that is not of the same content. Further, in storage systems adopting data deduplication technology, the data volume used by a user and the actual storage capacity required differs according to the volume of data that is of the same content.
As described, storage systems adopting data deduplication technology can record more data than storage systems that do not adopt data deduplication technology. Thus, administrators of storage systems adopting data deduplication technology can set lower charges for the same usage volume than the charges assessed for storage systems that do not adopt data deduplication technology.
In a state where low charges are set as described, if a user primarily uses data that does not coincide in terms of content, the charges assessed to the user are not proportionate with the volume of data used on the storage system, resulting in a possibility that overhead costs of storage system cannot be recovered. Thus, a billing method compatible with data deduplication technology has become necessary.
For example, Japanese Laid-Open Patent Publication No. 2006-11786 recites a deduplication method of a storage system that shares data, where a common disk is prepared and files that have been subject to deduplication in the form of “master+diff” for each file are stored. Thus, if the disk is shared by n persons, the volume of the disk used (≈charges) is 1/n. Japanese Laid-Open Patent Publication No. 2002-236809 recites a deduplication method in which documents are stored to a server and deduplication is performed in the form of a sharing of the documents. The latter publication further recites that if maintenance cost is a unit time cost of α (yen/KB), the size of document A is β(KB), and the number of users of document A is N (persons), charges are (α×β)/n. The more a file is shared, the lower the cost is to the users.
Nonetheless, in the method recited in Japanese Laid-Open Patent Publication No. 2006-11786, the deduplication method is performed by file, while charges are assessed by disk. In this case, the charges assessed to a user using a small portion of a disk and a user using nearly an entire disk are equivalent. Thus, a problem arises in that the degree to which the volume used by a user affects the disk capacity of the storage system is not reflected in the charges assessed to the user.
Furthermore, in Japanese Laid-Open Patent Publication No. 2002-236809, even if the background image is the same, if the text differs, the data is saved as a separate document file. Therefore, a problem arises in that the sharing count becomes inaccurate and the degree to which usable disk capacity of the storage system is affected by the usage volume of the user is reflected, with poor accuracy, on the charges assessed to the user.
Thus, with the conventional technologies, even when the sharing count of data is large, despite contributing to a reduction in the amount of disk space used, if the data size is large, the charges increase, arising in a mismatch. Similarly, even if data size is small, a small sharing count invites an increase in the amount of disk space consumed, arising again in a mismatch since the charges decrease. Therefore, a sense of unfairness in terms of billing may arise among users.